Collagen is the major structural protein in bone and other connective tissues, such as the gingivia in periodental ligament. Collagen fibers are the means by which the tooth is attached to the bone. During periodontitus, destruction of collagen takes place by active mammalian collagenase which is found at the site of active disease. Doxycycline, an inhibitor of collagenase, has been shown to be effective at non-antimicrobial doses in reducing elevated levels of collagenase associated with active periodontitus.